<template>
    <div class="pointers-container">
        <div id='a-box'>
            <canvas></canvas>
        </div>
    </div>
</template>


<script setup>
    import {onBeforeUnmount, onMounted, reactive} from 'vue';

    const emits = defineEmits(['mose'])
    const state = reactive({
        scrollHeight: 0
    })
    const handleScrollHeight = () => {
        state.scrollHeight = window.scrollY * 0.05
    }


    onMounted(() => {
        // 始化和获取WebGL上下文:
        const canvas = document.getElementsByTagName('canvas')[0];
        canvas.width = canvas.clientWidth;
        canvas.height = canvas.clientHeight;

        let config = {
            TEXTURE_DOWNSAMPLE: 1,
            DENSITY_DISSIPATION: 0.98,
            VELOCITY_DISSIPATION: 0.99,
            PRESSURE_DISSIPATION: 0.8,
            PRESSURE_ITERATIONS: 25,
            CURL: 28,
            SPLAT_RADIUS: 0.004
        };


        let pointers = [];
        let splatStack = [];

        const {gl, ext} = getWebGLContext(canvas);

        function getWebGLContext(canvas) {
            const params = {alpha: false, depth: false, stencil: false, antialias: false};

            let gl = canvas.getContext('webgl2', params);
            const isWebGL2 = !!gl;
            if (!isWebGL2)
                gl = canvas.getContext('webgl', params) || canvas.getContext('experimental-webgl', params);

            let halfFloat;
            let supportLinearFiltering;
            if (isWebGL2) {
                gl.getExtension('EXT_color_buffer_float');
                supportLinearFiltering = gl.getExtension('OES_texture_float_linear');
            } else {
                halfFloat = gl.getExtension('OES_texture_half_float');
                supportLinearFiltering = gl.getExtension('OES_texture_half_float_linear');
            }
            // let captureFolder = gl.addFolder('Capture');
            // captureFolder.addColor(0.0, 0.0, 0.0, 1.0);
            // gl.clearColor(0.0, 0.0, 0.0, 1.0);
            gl.clearColor(1.0, 1.0, 1.0, 1.0);

            const halfFloatTexType = isWebGL2 ? gl.HALF_FLOAT : halfFloat.HALF_FLOAT_OES;
            let formatRGBA;
            let formatRG;
            let formatR;

            if (isWebGL2) {
                formatRGBA = getSupportedFormat(gl, gl.RGBA16F, gl.RGBA, halfFloatTexType);
                formatRG = getSupportedFormat(gl, gl.RG16F, gl.RG, halfFloatTexType);
                formatR = getSupportedFormat(gl, gl.R16F, gl.RED, halfFloatTexType);
            } else {
                formatRGBA = getSupportedFormat(gl, gl.RGBA, gl.RGBA, halfFloatTexType);
                formatRG = getSupportedFormat(gl, gl.RGBA, gl.RGBA, halfFloatTexType);
                formatR = getSupportedFormat(gl, gl.RGBA, gl.RGBA, halfFloatTexType);
            }

            return {
                gl,
                ext: {
                    formatRGBA,
                    formatRG,
                    formatR,
                    halfFloatTexType,
                    supportLinearFiltering
                }
            };


        }

        function getSupportedFormat(gl, internalFormat, format, type) {
            if (!supportRenderTextureFormat(gl, internalFormat, format, type)) {
                switch (internalFormat) {

                    case gl.R16F:
                        return getSupportedFormat(gl, gl.RG16F, gl.RG, type);
                    case gl.RG16F:
                        return getSupportedFormat(gl, gl.RGBA16F, gl.RGBA, type);
                    default:
                        return null;
                }

            }

            return {
                internalFormat,
                format
            };

        }

        function supportRenderTextureFormat(gl, internalFormat, format, type) {
            let texture = gl.createTexture();
            gl.bindTexture(gl.TEXTURE_2D, texture);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
            gl.texImage2D(gl.TEXTURE_2D, 0, internalFormat, 4, 4, 0, format, type, null);

            let fbo = gl.createFramebuffer();
            gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);
            gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);

            const status = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
            if (status != gl.FRAMEBUFFER_COMPLETE)
                return false;
            return true;
        }

        function pointerPrototype() {
            this.id = -1;
            this.x = 0;
            this.y = 0;
            this.dx = 0;
            this.dy = 0;
            this.down = false;
            this.moved = false;
            this.color = [30, 0, 300];
        }

        pointers.push(new pointerPrototype());

        class GLProgram {
            constructor(vertexShader, fragmentShader) {
                this.uniforms = {};
                this.program = gl.createProgram();

                gl.attachShader(this.program, vertexShader);
                gl.attachShader(this.program, fragmentShader);
                gl.linkProgram(this.program);

                if (!gl.getProgramParameter(this.program, gl.LINK_STATUS))
                    throw gl.getProgramInfoLog(this.program);

                const uniformCount = gl.getProgramParameter(this.program, gl.ACTIVE_UNIFORMS);
                for (let i = 0; i < uniformCount; i++) {
                    const uniformName = gl.getActiveUniform(this.program, i).name;
                    this.uniforms[uniformName] = gl.getUniformLocation(this.program, uniformName);
                }
            }

            bind() {
                gl.useProgram(this.program);
            }
        }


        function compileShader(type, source) {
            const shader = gl.createShader(type);
            gl.shaderSource(shader, source);
            gl.compileShader(shader);

            if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS))
                throw gl.getShaderInfoLog(shader);

            return shader;
        }

        //********定义着色器程序  顶点着色器代码**********
        const baseVertexShader = compileShader(gl.VERTEX_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    attribute vec2 aPosition;
    varying vec2 vUv;
    varying vec2 vL;
    varying vec2 vR;
    varying vec2 vT;
    varying vec2 vB;
    uniform vec2 texelSize;

    void main () {
        vUv = aPosition * 0.5 + 0.5;
        vL = vUv - vec2(texelSize.x, 0.0);
        vR = vUv + vec2(texelSize.x, 0.0);
        vT = vUv + vec2(0.0, texelSize.y);
        vB = vUv - vec2(0.0, texelSize.y);
        gl_Position = vec4(aPosition, 0.0, 1.0);
    }
`);
        //定义着色器程序  // 清除着色器代码
        const clearShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    uniform sampler2D uTexture;
    uniform float value;

    void main () {
        gl_FragColor = value * texture2D(uTexture, vUv);
    }
`);

        const displayShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    uniform sampler2D uTexture;

    void main () {
       gl_FragColor = texture2D(uTexture, vUv);
        //  gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
    }
`);

        const splatShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    uniform sampler2D uTarget;
    uniform float aspectRatio;
    uniform vec3 color;
    uniform vec2 point;
    uniform float radius;

    void main () {
        vec2 p = vUv - point.xy;
        p.x *= aspectRatio;
        vec3 splat = exp(-dot(p, p) / radius) * color;
        vec3 base = texture2D(uTarget, vUv).xyz;
        gl_FragColor = vec4(base + splat, 1.0);
    }
`);

        const advectionManualFilteringShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    uniform sampler2D uVelocity;
    uniform sampler2D uSource;
    uniform vec2 texelSize;
    uniform float dt;
    uniform float dissipation;

    vec4 bilerp (in sampler2D sam, in vec2 p) {
        vec4 st;
        st.xy = floor(p - 0.5) + 0.5;
        st.zw = st.xy + 1.0;
        vec4 uv = st * texelSize.xyxy;
        vec4 a = texture2D(sam, uv.xy);
        vec4 b = texture2D(sam, uv.zy);
        vec4 c = texture2D(sam, uv.xw);
        vec4 d = texture2D(sam, uv.zw);
        vec2 f = p - st.xy;
        return mix(mix(a, b, f.x), mix(c, d, f.x), f.y);
    }

    void main () {
        vec2 coord = gl_FragCoord.xy - dt * texture2D(uVelocity, vUv).xy;
        gl_FragColor = dissipation * bilerp(uSource, coord);
        gl_FragColor.a = 1.0;
    }
`);

        const advectionShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    uniform sampler2D uVelocity;
    uniform sampler2D uSource;
    uniform vec2 texelSize;
    uniform float dt;
    uniform float dissipation;

    void main () {
        vec2 coord = vUv - dt * texture2D(uVelocity, vUv).xy * texelSize;
        gl_FragColor = dissipation * texture2D(uSource, coord);
        gl_FragColor.a = 1.0;
    }
`);

        const divergenceShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    varying vec2 vL;
    varying vec2 vR;
    varying vec2 vT;
    varying vec2 vB;
    uniform sampler2D uVelocity;

    vec2 sampleVelocity (in vec2 uv) {
        vec2 multiplier = vec2(1.0, 1.0);
        if (uv.x < 0.0) { uv.x = 0.0; multiplier.x = -1.0; }
        if (uv.x > 1.0) { uv.x = 1.0; multiplier.x = -1.0; }
        if (uv.y < 0.0) { uv.y = 0.0; multiplier.y = -1.0; }
        if (uv.y > 1.0) { uv.y = 1.0; multiplier.y = -1.0; }
        return multiplier * texture2D(uVelocity, uv).xy;
    }

    void main () {
        float L = sampleVelocity(vL).x;
        float R = sampleVelocity(vR).x;
        float T = sampleVelocity(vT).y;
        float B = sampleVelocity(vB).y;
        float div = 0.5 * (R - L + T - B);
        gl_FragColor = vec4(div, 0.0, 0.0, 1.0);
    }
`);

        const curlShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    varying vec2 vL;
    varying vec2 vR;
    varying vec2 vT;
    varying vec2 vB;
    uniform sampler2D uVelocity;

    void main () {
        float L = texture2D(uVelocity, vL).y;
        float R = texture2D(uVelocity, vR).y;
        float T = texture2D(uVelocity, vT).x;
        float B = texture2D(uVelocity, vB).x;
        float vorticity = R - L - T + B;
        gl_FragColor = vec4(vorticity, 0.0, 0.0, 1.0);
    }
`);

        const vorticityShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    varying vec2 vT;
    varying vec2 vB;
    uniform sampler2D uVelocity;
    uniform sampler2D uCurl;
    uniform float curl;
    uniform float dt;

    void main () {
        float T = texture2D(uCurl, vT).x;
        float B = texture2D(uCurl, vB).x;
        float C = texture2D(uCurl, vUv).x;
        vec2 force = vec2(abs(T) - abs(B), 0.0);
        force *= 1.0 / length(force + 0.00001) * curl * C;
        vec2 vel = texture2D(uVelocity, vUv).xy;
        gl_FragColor = vec4(vel + force * dt, 0.0, 1.0);
    }
`);

        const pressureShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    varying vec2 vL;
    varying vec2 vR;
    varying vec2 vT;
    varying vec2 vB;
    uniform sampler2D uPressure;
    uniform sampler2D uDivergence;

    vec2 boundary (in vec2 uv) {
        uv = min(max(uv, 0.0), 1.0);
        return uv;
    }

    void main () {
        float L = texture2D(uPressure, boundary(vL)).x;
        float R = texture2D(uPressure, boundary(vR)).x;
        float T = texture2D(uPressure, boundary(vT)).x;
        float B = texture2D(uPressure, boundary(vB)).x;
        float C = texture2D(uPressure, vUv).x;
        float divergence = texture2D(uDivergence, vUv).x;
        float pressure = (L + R + B + T - divergence) * 0.25;
        gl_FragColor = vec4(pressure, 0.0, 0.0, 1.0);
    }
`);

        const gradientSubtractShader = compileShader(gl.FRAGMENT_SHADER, `
    precision highp float;
    precision mediump sampler2D;

    varying vec2 vUv;
    varying vec2 vL;
    varying vec2 vR;
    varying vec2 vT;
    varying vec2 vB;
    uniform sampler2D uPressure;
    uniform sampler2D uVelocity;

    vec2 boundary (in vec2 uv) {
        uv = min(max(uv, 0.0), 1.0);
        return uv;
    }

    void main () {
        float L = texture2D(uPressure, boundary(vL)).x;
        float R = texture2D(uPressure, boundary(vR)).x;
        float T = texture2D(uPressure, boundary(vT)).x;
        float B = texture2D(uPressure, boundary(vB)).x;
        vec2 velocity = texture2D(uVelocity, vUv).xy;
        velocity.xy -= vec2(R - L, T - B);
        gl_FragColor = vec4(velocity, 0.0, 1.0);
    }
`);
        //********定义着色器程序结束 **********

        // 初始化帧缓冲对象：
        let textureWidth;
        let textureHeight;
        let density;
        let velocity;
        let divergence;
        let curl;
        let pressure;
        initFramebuffers();

        // 创建着色器程序对象
        const clearProgram = new GLProgram(baseVertexShader, clearShader);
        const displayProgram = new GLProgram(baseVertexShader, displayShader);
        const splatProgram = new GLProgram(baseVertexShader, splatShader);
        const advectionProgram = new GLProgram(baseVertexShader, ext.supportLinearFiltering ? advectionShader : advectionManualFilteringShader);
        const divergenceProgram = new GLProgram(baseVertexShader, divergenceShader);
        const curlProgram = new GLProgram(baseVertexShader, curlShader);
        const vorticityProgram = new GLProgram(baseVertexShader, vorticityShader);
        const pressureProgram = new GLProgram(baseVertexShader, pressureShader);
        const gradienSubtractProgram = new GLProgram(baseVertexShader, gradientSubtractShader);


        function initFramebuffers() {
            textureWidth = gl.drawingBufferWidth >> config.TEXTURE_DOWNSAMPLE;
            textureHeight = gl.drawingBufferHeight >> config.TEXTURE_DOWNSAMPLE;

            const texType = ext.halfFloatTexType;
            const rgba = ext.formatRGBA;
            const rg = ext.formatRG;
            const r = ext.formatR;

            density = createDoubleFBO(2, textureWidth, textureHeight, rgba.internalFormat, rgba.format, texType, ext.supportLinearFiltering ? gl.LINEAR : gl.NEAREST);
            velocity = createDoubleFBO(0, textureWidth, textureHeight, rg.internalFormat, rg.format, texType, ext.supportLinearFiltering ? gl.LINEAR : gl.NEAREST);
            divergence = createFBO(4, textureWidth, textureHeight, r.internalFormat, r.format, texType, gl.NEAREST);
            curl = createFBO(5, textureWidth, textureHeight, r.internalFormat, r.format, texType, gl.NEAREST);
            pressure = createDoubleFBO(6, textureWidth, textureHeight, r.internalFormat, r.format, texType, gl.NEAREST);
        }


        // 定义和创建帧缓冲对象和纹理
        function createFBO(texId, w, h, internalFormat, format, type, param) {
            gl.activeTexture(gl.TEXTURE0 + texId);
            let texture = gl.createTexture();
            gl.bindTexture(gl.TEXTURE_2D, texture);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, param);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, param);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
            gl.texImage2D(gl.TEXTURE_2D, 0, internalFormat, w, h, 0, format, type, null);

            let fbo = gl.createFramebuffer();
            gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);
            gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);
            gl.viewport(0, 0, w, h);
            gl.clear(gl.COLOR_BUFFER_BIT);

            return [texture, fbo, texId];
        }

        function createDoubleFBO(texId, w, h, internalFormat, format, type, param) {
            let fbo1 = createFBO(texId, w, h, internalFormat, format, type, param);
            let fbo2 = createFBO(texId + 1, w, h, internalFormat, format, type, param);

            return {
                get read() {
                    return fbo1;
                },
                get write() {
                    return fbo2;
                },
                swap() {
                    let temp = fbo1;
                    fbo1 = fbo2;
                    fbo2 = temp;
                }
            };

        }


        const blit = (() => {
            gl.bindBuffer(gl.ARRAY_BUFFER, gl.createBuffer());
            gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1, -1, -1, 1, 1, 1, 1, -1]), gl.STATIC_DRAW);
            gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, gl.createBuffer());
            gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array([0, 1, 2, 0, 2, 3]), gl.STATIC_DRAW);
            gl.vertexAttribPointer(0, 2, gl.FLOAT, false, 0, 0);
            gl.enableVertexAttribArray(0);

            return destination => {
                gl.bindFramebuffer(gl.FRAMEBUFFER, destination);
                gl.drawElements(gl.TRIANGLES, 6, gl.UNSIGNED_SHORT, 0);
            };
        })();

        let lastTime = Date.now();
        multipleSplats(parseInt(Math.random() * 20) + 5);
        update();

        // 主渲染循环和计算流体效果：
        function update() {
            resizeCanvas();


            const dt = Math.min((Date.now() - lastTime) / 1000, 0.016);
            lastTime = Date.now();

            gl.viewport(0, 0, textureWidth, textureHeight);

            if (splatStack.length > 0)
                multipleSplats(splatStack.pop());

            advectionProgram.bind();
            gl.uniform2f(advectionProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
            gl.uniform1i(advectionProgram.uniforms.uVelocity, velocity.read[2]);
            gl.uniform1i(advectionProgram.uniforms.uSource, velocity.read[2]);
            gl.uniform1f(advectionProgram.uniforms.dt, dt);
            gl.uniform1f(advectionProgram.uniforms.dissipation, config.VELOCITY_DISSIPATION);
            blit(velocity.write[1]);
            velocity.swap();

            gl.uniform1i(advectionProgram.uniforms.uVelocity, velocity.read[2]);
            gl.uniform1i(advectionProgram.uniforms.uSource, density.read[2]);
            gl.uniform1f(advectionProgram.uniforms.dissipation, config.DENSITY_DISSIPATION);
            blit(density.write[1]);
            density.swap();

            for (let i = 0; i < pointers.length; i++) {
                const pointer = pointers[i];
                if (pointer.moved) {
                    splat(pointer.x, pointer.y, pointer.dx, pointer.dy, pointer.color);
                    pointer.moved = false;
                }
            }

            curlProgram.bind();
            gl.uniform2f(curlProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
            gl.uniform1i(curlProgram.uniforms.uVelocity, velocity.read[2]);
            blit(curl[1]);

            vorticityProgram.bind();
            gl.uniform2f(vorticityProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
            gl.uniform1i(vorticityProgram.uniforms.uVelocity, velocity.read[2]);
            gl.uniform1i(vorticityProgram.uniforms.uCurl, curl[2]);
            gl.uniform1f(vorticityProgram.uniforms.curl, config.CURL);
            gl.uniform1f(vorticityProgram.uniforms.dt, dt);
            blit(velocity.write[1]);
            velocity.swap();

            divergenceProgram.bind();
            gl.uniform2f(divergenceProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
            gl.uniform1i(divergenceProgram.uniforms.uVelocity, velocity.read[2]);
            blit(divergence[1]);

            clearProgram.bind();
            let pressureTexId = pressure.read[2];
            gl.activeTexture(gl.TEXTURE0 + pressureTexId);
            gl.bindTexture(gl.TEXTURE_2D, pressure.read[0]);
            gl.uniform1i(clearProgram.uniforms.uTexture, pressureTexId);
            gl.uniform1f(clearProgram.uniforms.value, config.PRESSURE_DISSIPATION);
            blit(pressure.write[1]);
            pressure.swap();

            pressureProgram.bind();
            gl.uniform2f(pressureProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
            gl.uniform1i(pressureProgram.uniforms.uDivergence, divergence[2]);
            pressureTexId = pressure.read[2];
            gl.uniform1i(pressureProgram.uniforms.uPressure, pressureTexId);
            gl.activeTexture(gl.TEXTURE0 + pressureTexId);
            for (let i = 0; i < config.PRESSURE_ITERATIONS; i++) {
                gl.bindTexture(gl.TEXTURE_2D, pressure.read[0]);
                blit(pressure.write[1]);
                pressure.swap();
            }

            gradienSubtractProgram.bind();
            gl.uniform2f(gradienSubtractProgram.uniforms.texelSize, 1.0 / textureWidth, 1.0 / textureHeight);
            gl.uniform1i(gradienSubtractProgram.uniforms.uPressure, pressure.read[2]);
            gl.uniform1i(gradienSubtractProgram.uniforms.uVelocity, velocity.read[2]);
            blit(velocity.write[1]);
            velocity.swap();

            gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
            displayProgram.bind();
            gl.uniform1i(displayProgram.uniforms.uTexture, density.read[2]);
            blit(null);

            requestAnimationFrame(update);
        }

        function splat(x, y, dx, dy, color) {
            splatProgram.bind();
            gl.uniform1i(splatProgram.uniforms.uTarget, velocity.read[2]);
            gl.uniform1f(splatProgram.uniforms.aspectRatio, canvas.width / canvas.height);
            gl.uniform2f(splatProgram.uniforms.point, x / canvas.width, 1.0 - y / canvas.height);
            gl.uniform3f(splatProgram.uniforms.color, dx, -dy, 1.0);
            gl.uniform1f(splatProgram.uniforms.radius, config.SPLAT_RADIUS);
            blit(velocity.write[1]);
            velocity.swap();

            gl.uniform1i(splatProgram.uniforms.uTarget, density.read[2]);
            gl.uniform3f(splatProgram.uniforms.color, color[0] * 0.3, color[1] * 0.3, color[2] * 0.3);
            blit(density.write[1]);
            density.swap();
        }

        function multipleSplats(amount) {
            for (let i = 0; i < amount; i++) {
                const color = [Math.random() * 10, Math.random() * 10, Math.random() * 10];
                const x = canvas.width * Math.random();
                const y = canvas.height * Math.random();
                const dx = 1000 * (Math.random() - 0.5);
                const dy = 1000 * (Math.random() - 0.5);
                splat(x, y, dx, dy, color);
            }
        }

        function resizeCanvas() {
            if (canvas.width != canvas.clientWidth || canvas.height != canvas.clientHeight) {
                canvas.width = canvas.clientWidth;
                canvas.height = canvas.clientHeight;
                initFramebuffers();
            }
        }

        canvas.addEventListener('mousemove', e => {
            pointers[0].moved = pointers[0].down;
            pointers[0].dx = (e.offsetX - pointers[0].x) * 10.0;
            pointers[0].dy = (e.offsetY - pointers[0].y) * 10.0;
            pointers[0].x = e.offsetX;
            pointers[0].y = e.offsetY;
        });

        canvas.addEventListener('touchmove', e => {
            e.preventDefault();
            const touches = e.targetTouches;
            for (let i = 0; i < touches.length; i++) {
                let pointer = pointers[i];
                pointer.moved = pointer.down;
                pointer.dx = (touches[i].pageX - pointer.x) * 10.0;
                pointer.dy = (touches[i].pageY - pointer.y) * 10.0;
                pointer.x = touches[i].pageX;
                pointer.y = touches[i].pageY;
            }
        }, false);

        canvas.addEventListener('mousemove', () => {
            pointers[0].down = true;
            pointers[0].color = [Math.random() + 0.2, Math.random() + 0.2, Math.random() + 0.2];
        });

        canvas.addEventListener('touchstart', e => {
            e.preventDefault();
            const touches = e.targetTouches;
            for (let i = 0; i < touches.length; i++) {
                if (i >= pointers.length)
                    pointers.push(new pointerPrototype());

                pointers[i].id = touches[i].identifier;
                pointers[i].down = true;
                pointers[i].x = touches[i].pageX;
                pointers[i].y = touches[i].pageY;
                pointers[i].color = [Math.random() + 0.2, Math.random() + 0.2, Math.random() + 0.2];
            }
        });

        window.addEventListener('mouseleave', () => {
            pointers[0].down = false;
        });

        window.addEventListener('touchend', e => {
            const touches = e.changedTouches;
            for (let i = 0; i < touches.length; i++)
                for (let j = 0; j < pointers.length; j++)
                    if (touches[i].identifier == pointers[j].id)
                        pointers[j].down = false;
        });


        window.addEventListener('scroll', handleScrollHeight);
    })


    onBeforeUnmount(() => {
        window.removeEventListener('scroll', handleScrollHeight);
    });

</script>


<style scoped>
    .pointers-container {
        font-family: courier new;
        height: 110vh;
        width: 100%;
        position: relative;

        #a-box {
            margin: 0;
            padding: 0;
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;
            width: 100%;
            height: 100%;

            canvas {
                width: 100%;
                height: 100%;
            }
        }
    }
</style>
